1. Field of the Invention
The present invention relates generally to transceivers and, more particularly, to built-in calibration structures for transceivers.
2. Description of the Related Art
The flexibility, power and performance of digital transceivers have caused them to become an essential part of mobile radio systems, cellular telephone systems, paging systems, automotive entertainment systems and military communications.
Digital transceivers are typically complex systems and their performance is a function of a number of system parameters (e.g., transmitter gain, receiver gain, receiver noise, receiver intermodulation distortion and receiver dynamic range). Periodic monitoring and recalibration of these parameters is desirable if transceiver performance is to be maintained at a high level.
Monitoring and recalibration costs can be greatly reduced if the transceiver includes significant built-in test and calibration structures. These structures can also reduce initial manufacturing cost because they can expose problems at early manufacturing stages and can reduce the need for expensive test equipment. These structures can also enhance customer satisfaction because they reduce the cost and time required to maintain transceivers in a high-performance state.
Various built-in, self-test (BIST) systems have been proposed. For example, a BIST system for mixed analog-digital (MAD) structures was described by M. F. Toner, et al. (Toner M. F., et al., "On the Practical Implementation of Mixed Analog-Digital BIST", IEEE 1995 Custom Integrated Circuits Conference, March, 1991, pp. 525-528). In this BIST system, a precision analog test stimulus was generated with an over-sampling oscillator. The test stimulus included single and/or multiple sine-waves with digitally-programmable amplitudes, frequencies and phases. The analog output was imbedded in a pulse-density modulated digital bit stream.
Measurement of responses to the test stimulus was facilitated with an analog-to-digital converter (ADC) whose output was coupled through a narrow-band digital filter. Analog signal and noise powers were extracted by applying analog waveforms to the ADC, selecting a passband frequency for the digital filter and computing the sum of squares of samples emerging from the filter.
In a sequence of operations, the oscillator was used to calibrate the ADC which was then used to measure analog signals. Toner, et al. suggested that the ADC could be used to calibrate an analog-to-digital converter (DAC) and the two converters used as a precision analog stimulus and volt-meter.
Although the suggestion of an ADC and a DAC as analog stimulus and volt-meter is helpful, it fails to enable the calibration and correction of complex systems such as transceivers.